A quantum key distribution (QKD) system uses quantum mechanics to guarantee secure communications in a quantum communications system. For example, the QKD system transmits cryptographic key data encoded in quantum states of individual optical photons. In this example, an advantage of the QKD system is that, it allows secure transmission of a key data over unsecured optical links with security guaranteed by fundamental quantum properties of light rather than by computational complexity of certain mathematical functions. For example, the quantum property may utilize single photons that cannot be split into smaller pieces. In this example, a possible interception by a third party may allow diversion of the photons or simply the photons may not arrive at intended destinations.
The QKD system is used to produce and distribute a key and not to transmit any message data. This key may then be used with any chosen encryption algorithm to encrypt and decrypt a message, which may be transmitted over a standard communications channel.
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